Halogen-containing phosphate esters are compounds widely used in various areas including chemical and pharmaceutical industries as resin additives such as flame retardants and plasticizers, intermediates for medicaments or pesticides and the like. When those halogen-containing phosphate esters which are solid at room temperature, among others, are produced, the products are effectively purified by the crystallization processes used to increase the quality of the products. However, when phosphate esters are produced by using crystallization processes, waste water which contains phosphorus-containing organic pollutants is generally generated.
Waste water from chemical plants and organic sewage such as drainage generally contain COD materials and phosphorus. The COD material refers to any organic material which indicates certain COD (i.e., chemical oxygen demand) in an aqueous solution. Since phosphorus has a considerable effect on the environment, effective removal of phosphorus from the waste water or organic sewage is important. Biological treatment or biodegradation has been known as one of the treatment methods for the waste water and organic sewage. Japanese Laid-open Patent Publications (Kokai) Nos. 7-275891 and 8-24872 describe processes in which phosphorus-containing waste water is biologically treated in an activated sludge treatment device to remove phosphorus from the waste water.
However, it has been difficult to effectively remove phosphorus-containing organic pollutants which are generated during production of halogen-containing phosphate esters, from the waste water, by conventional biodegradation. One of the reasons for such difficulty is that the pollutants contained in the waste water from the process for producing a halogen-containing phosphate ester, unlike the waste water from a process for producing a halogen-free phosphate ester, may include halogenated organic phosphorus in addition to inorganic phosphorus. Moreover, in the case that the waste water contains additional materials such as catalyst residue and unreacted raw materials, the biodegradation is expected to become more difficult. Furthermore, such waste water may adversely affect the natural environment as well as health of neighborhood and workers dealing with the treatment. In addition, devices for the biodegradation are generally those of a very large scale which are difficult to control. Moreover, treatment of the sludge involved in the biodegradation requires high cost.
The objective of the present invention is to provide a clean and safe process for producing a halogen-containing phosphate ester without generating deleterious materials, in which pollutants, especially phosphorus, are removed from waste water generated during production of the halogen-containing phosphate ester.